Systems for applying a thermal barrier coating to a superalloy substrate

ABSTRACT

Systems for applying a thermal barrier coating to a superalloy substrate including at least one target for supplying a material for making the thermal barrier coating; at least one laser operably directed toward the target for liberating atomic particles from the target; and a plasma torch for generating a plasma for accelerating and depositing the atomic particles onto the superalloy substrate as the thermal barrier coating where the superalloy substrate is a nickel based superalloy or a cobalt based superalloy.

TECHNICAL FIELD

Embodiments described herein generally relate to systems for applying athermal barrier coating to a superalloy substrate. More particularly,embodiments herein generally relate to systems for carrying out laserassisted plasma coating at atmospheric pressure for applying a thermalbarrier coating to a superalloy substrate.

BACKGROUND OF THE INVENTION

Increasingly stringent demands are being imposed on the efficacy of gasturbine engines employed in the aerospace and power generationindustries. This demand is driven by the requirement to reduce theconsumption of fossil fuels, and in turn, operating costs. One way toimprove turbine efficiency is to increase the operating temperature inthe turbine section of the engine. However, with increased operatingtemperatures comes an increased demand on materials used in the turbinesection. Not only must these materials be able to withstand the higheroperating temperatures (from about 800° C. to about 1500° C.), but theymust also endure increased mechanical stresses, corrosion, erosion, andother severe operating conditions, while continuing to fulfill lifetimerequirements expected by the industry. This can be accomplished throughthe use of thermal barrier coatings (TBCs) applied to the hightemperature component.

Conventional practices often utilize plasma spray or electron beamphysical vapor deposition (EBPVD) to apply the high temperature TBCs,both of which can be problematic. For example, plasma spray can producehighly porous coatings having lower erosion and impact resistance thanEBPVD. Such plasma sprayed coatings can be susceptible to plugging upthe cooling holes of turbine components to which they are applied. WhileEBPVD can produce more desirable coatings, it is an expensive processbecause it is carried out under a high vacuum and has higher equipmentcosts.

Accordingly, there remains a need for systems that are capable ofproducing coatings that are structurally similar to those resulting fromEBPVD, without the costly vacuum and equipment requirements set forthpreviously.

BRIEF DESCRIPTION OF THE INVENTION

Embodiments herein generally relate to systems for applying a thermalbarrier coating to a superalloy substrate comprising: at least onetarget for supplying a material for making the thermal barrier coating;at least one laser operably directed toward the target for liberatingatomic particles from the target; and a plasma torch for generating aplasma for accelerating and depositing the atomic particles onto thesuperalloy substrate as the thermal barrier coating wherein thesuperalloy substrate is a nickel based superalloy or a cobalt basedsuperalloy.

Embodiments herein also generally relate to systems for applying athermal barrier coating to a superalloy substrate comprising: twotargets for supplying a material for making the thermal barrier coating;two lasers, one laser operably directed toward each of the targets forliberating atomic particles from the targets; and a plasma torch forgenerating a plasma for accelerating and depositing the atomic particlesonto the superalloy substrate as the thermal barrier coating wherein thesuperalloy substrate is a nickel based superalloy or a cobalt basedsuperalloy.

Embodiments herein also generally relate to systems for applying athermal barrier coating to a superalloy substrate comprising: twotargets for supplying a material for making the thermal barrier coating,a first target comprising zirconium oxide and a second target comprisingyttrium oxide; two Nd:YAG lasers, one laser operably directed towardeach of the targets for liberating atomic particles from the targets;and a plasma torch for generating a plasma for accelerating anddepositing the atomic particles onto the superalloy substrate as thethermal barrier coating comprising about 92% by weight zirconium oxideand about 8% by weight yttrium oxide.

These and other features, aspects and advantages will become evident tothose skilled in the art from the following disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming the invention, it is believed that theembodiments set forth herein will be better understood from thefollowing description in conjunction with the accompanying figures, inwhich like reference numerals identify like elements.

FIG. 1 is a schematic cross-sectional representation of one embodimentof a laser assisted plasma coating at atmospheric pressure (LAPCAP)system in accordance with the description herein; and

FIG. 2 is a schematic cross-sectional representation of an alternateembodiment of a LAPCAP system in accordance with the description herein.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments described herein generally relate to systems for carryingout laser assisted plasma coating at atmospheric pressure (LAPCAP) forapplying a thermal barrier coating to a superalloy substrate. While thesystems herein are designated “at atmospheric pressure,” they should notbe limited to such. More specifically, the LAPCAP system may be utilizedat near atmospheric pressure (e.g. about 0.5 Atm to about 3 Atm).

In general, the LAPCAP system involves using at least one pulsed laserto liberate atomic particles from at least one target, and then feedingthose atomic particles into a plasma for deposition onto a substrate toform a thermal barrier coating. As used herein, “liberate” can refer toany of ablating, vaporizing, melting, or some combination thereof. Whilethe coatings described herein may be used on any substrate exposed tohigh temperature environments (from about 800° C. to about 1500° C.),such coatings are particularly suited for use on components in theturbine section of a gas turbine engine.

In one embodiment, and as shown in FIG. 1, LAPCAP system 10 cangenerally comprise a plasma torch 16, at least one target 12, and atleast one laser 14. Plasma torch 16 can include a gas stream 18 thatfeeds into a discharge tube 20 having a plurality of inductively coupledplasma (ICP) coils 22 that can serve as a radio frequency generator, asset forth below.

More particularly, gas stream 18 can feed into discharge tube 20 to helpgenerate plasma 24 and can comprise any gas suitable for carrying outconventional plasma spray processes, which in one embodiment, can beselected from argon, nitrogen, hydrogen, helium, oxygen, andcombinations thereof. In particular, as gas stream 18 feeds intodischarge tube 20, the radio frequency field generated by ICP coils 22can be activated. As gas stream 18 passes through discharge tube 20,adjacent to ICP coils, gas stream 18 can become electrically conductive,and form plasma 24. At low flow rates (e.g. about 0.5 L/minute, forexample) the plasma can be more stationary, whereas at higher gas flowrates (e.g. about 30 L/minute, for example) the plasma can take the formof a jet. It will be understood that a variety of flow rates, both aboveand below those provided herein, can also be utilized to alter thesurface morphology and of the thermal barrier coatings. In an alternateembodiment, plasma 24 can be created by a microwave discharge (notshown) instead of, or in conjunction with, ICP coils 22.

Target 12 may comprise any material capable of being atomized by laser14 and suitable for use as a thermal barrier coating, such as forexample, ceramic materials and metallic materials. As used herein,“ceramic materials” can include zirconium oxide, yttrium oxide, aluminaand pre-alloyed combinations thereof, while “metallic materials” mayinclude zirconium, yttrium, aluminum, and combinations thereof.

In the embodiment shown in FIG. 1, target 12 can be positioned belowdischarge tube 20 of plasma torch 16, adjacent to plasma 24, and securedin place using any suitable means. In an alternate embodiment, target 12can be placed inside of plasma torch 16, or be positioned to permittarget 12 to replace and function as discharge tube 20. Laser 14 can beoperably directed toward target 12 such that during operation, laser 14can strike target 12 to liberate atomic particles 26, which can combinein the proper proportion in plasma 24 needed to make the desired TBC.Plasma 24 can then be used to accelerate and deposit atomic particles 26onto substrate 28 as set forth below. When metallic materials are usedas target 12, reactive gases, such as oxygen and nitrogen, can be usedto oxidize or nitrodize the atomic particles to obtain the desiredcoating composition and properties. Such gases can be added to theLAPCAP system or come from the atmosphere.

Several varieties of solid state pulsed lasers having sufficient energyto liberate the atomic particles from the target can be utilized,including, but not limited to, neodymium-doped yttrium aluminum garnet(Nd:YAG) lasers. Because of the adjacency of target 12 to plasma 24,atomic particles 26 are fed into plasma 24 as they are liberated. Plasma24 can then accelerate the atomic particles, forcing them onto substrate28, where they can deposit as TBC 30. Variation in the combination oflaser operating parameters, including laser pulse length, laser pulseenergy, laser intensity, and laser spot size can allow the atomicparticle flux and distribution to be tailored to achieve the desiredcoating composition and properties. Generally, pulsed laser 14 can havea pulse length of from about 5 femtoseconds to about 100 microseconds, apulse energy of from about 0.001 mJ to about 10 J, an intensity of fromabout 10⁴ W/cm² to about 10¹⁵ W/cm², and a laser spot size ranging fromabout 1 micrometer to about 5 millimeters.

While a variety of substrates 28 can be used in conjunction with theembodiments herein, in one embodiment, substrate 28 may be selected fromsuperalloys suitable for use in high temperature (from about 800° C. toabout 1500° C.) environments, such as those present in the turbinesection of a gas turbine engine. Some examples of such superalloys caninclude, but should not be limited to, nickel based superalloys, andcobalt based superalloys. In order to achieve the desired TBC 30thickness, which can range from about 50 microns to about 750 microns,substrate 28 can be moved beneath a stationary LAPCAP system 10 to buildup layers of TBC 30. In an alternate embodiment, substrate 28 can bestationary while the system 10 moves as needed using a pre-programmedrobotic armature (not shown). The embodiments herein can result in thedeposition of a TBC that has a columnar microstructure similar to thatof coatings obtained using EBPVD. More specifically, the TBCs herein canhave a column width of from about 0.5 microns to about 60 microns, andan intra column porosity of from about 0% to about 9%. In oneembodiment, the TBC can comprise smaller diameter columns and about 0%porosity.

In an alternate embodiment, more than one target and more than one lasercan be used. As used here, “lasers” can refer to either multipleindependent lasers, or alternately, one laser split into multiple beams.In such instances, each target may comprise the same or differentmaterials (such as in the exemplary embodiment below). It will beunderstood that one laser, i.e. either an independent laser, or a splitlaser beam, can be operably directed toward each target to liberateatomic particles therefrom.

By way of example and not limitation, and as shown in FIG. 2, LAPCAPsystem 110 can comprise a gas stream 18, which in one embodiment can beargon, two pulsed Nd:YAG lasers 14, two targets comprising ceramicmaterials, a first target 112 comprising ZrO₂, and a second target 212comprising Y₂O₃. Gas stream 18 can comprise a gas flow of from about0.05 L/minute to about 0.6 L/minute. In this embodiment, pulsed lasers14 can have a pulse length of from about 5 ns to about 10 ns, a pulseenergy of about 10 mJ, an intensity of from about 10⁷ to about 10⁸W/cm², and a laser spot size ranging from about 1 micrometer to about 2millimeters. This particular combination of laser operating parameterscan liberate atomic particles 126 of zirconium, oxygen, and yttria,which can be deposited onto a combination nickel based, and cobaltbased, superalloy substrate 28 as a thermal barrier coating 130comprising about 92% by weight ZrO₂ and about 8% by weight Y₂O₃ andhaving a thickness of from about 50 microns to about 750 microns. Thoseskilled in the art will understand that this is an example of onepossible system and that other systems of varying parameters are withinthe scope of the present embodiments.

The embodiments described herein differ from conventional processes.Particularly, unlike EBPVD, LAPCAP does not require the use of costlyvacuum pumps, and particle generation, acceleration, and deposition canbe accomplished using a single apparatus. However, in spite of thesedifferences, LAPCAP can produce coatings having a columnarmicrostructure that is similar to coatings made using EBPVD. This ispossible since LAPCAP deposition occurs on an atomic level. The resultis a TBC that can be less susceptible to impact and erosion damage thancoatings produced using conventional plasma spray processes.Additionally, the clogging of cooling holes that can occur with plasmaspray can be greatly reduced or eliminated using LAPCAP.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to make and use the invention. The patentable scope of the inventionis defined by the claims, and may include other examples that occur tothose skilled in the art. Such other examples are intended to be withinthe scope of the claims if they have structural elements that do notdiffer from the literal language of the claims, or if they includeequivalent structural elements with insubstantial differences from theliteral language of the claims.

1. A system for applying a thermal barrier coating to a superalloysubstrate comprising: at least one target for supplying a material formaking the thermal barrier coating; at least one laser operably directedtoward the target for liberating atomic particles from the target; and aplasma torch for generating a plasma for accelerating and depositing theatomic particles onto the superalloy substrate as the thermal barriercoating wherein the superalloy substrate is a nickel based superalloy ora cobalt based superalloy.
 2. The system of claim 1 wherein the plasmatorch comprises a gas stream that feeds into a discharge tube thatactivates the gas stream and creates the plasma.
 3. The system of claim2 wherein the discharge tube comprises a plurality of inductivelycoupled plasma coils or a microwave, for generating a radio frequencyfield to activate the gas stream and create the plasma.
 4. The system ofclaim 3 wherein the gas stream comprises a gas selected from the groupconsisting of argon, nitrogen, hydrogen, helium, oxygen, andcombinations thereof.
 5. The system of claim 4 wherein the material ofthe target is a ceramic material selected from the group consisting ofzirconium oxide, yttrium oxide, alumina, and pre-alloyed combinationsthereof; or a metallic material selected from the group consisting ofzirconium, yttrium, aluminum, and combinations thereof.
 6. The system ofclaim 5 wherein the laser comprises a solid state pulsed laser.
 7. Thesystem of claim 6 wherein the coating is tailored by varying any one ormore operating parameter selected from the group consisting of laserpulse length, laser pulse energy, laser intensity, and laser spot size.8. The system of claim 7 wherein: the laser pulse length is from about 5femtoseconds to about 100 microseconds; the laser pulse energy is fromabout 0.001 mJ to about 10 J; the laser intensity is from about 10⁴W/cm² to about 10¹⁵ W/cm²; and the laser spot size is from about 1micrometer to about 5 millimeters.
 9. The system of claim 8 wherein thethermal barrier coating comprises a thickness of from about 50 micronsto about 750 microns.
 10. A system for applying a thermal barriercoating to a superalloy substrate comprising: two targets for supplyinga material for making the thermal barrier coating; two lasers, one laseroperably directed toward each of the targets for liberating atomicparticles from the targets; and a plasma torch for generating a plasmafor accelerating and depositing the atomic particles onto the superalloysubstrate as the thermal barrier coating wherein the superalloysubstrate is a nickel based superalloy or a cobalt based superalloy. 11.The system of claim 10 wherein the plasma torch comprises a gas streamthat feeds into a discharge tube that activates the gas stream andcreates the plasma.
 12. The system of claim 11 wherein the dischargetube comprises a plurality of inductively coupled plasma coils or amicrowave, for generating a radio frequency field to activate the gasstream and create the plasma.
 13. The system of claim 12 wherein the gasstream comprises a gas selected from the group consisting of argon,nitrogen, hydrogen, helium, oxygen, and combinations thereof.
 14. Thesystem of claim 13 wherein the material of the target is a ceramicmaterial selected from the group consisting of zirconium oxide, yttriumoxide, alumina, and pre-alloyed combinations thereof; or a metallicmaterial selected from the group consisting of zirconium, yttrium,aluminum, and combinations thereof.
 15. The system of claim 14 whereineach target comprises the same material.
 16. The system of claim 15wherein the lasers comprise solid state pulsed lasers.
 17. The system ofclaim 16 wherein the coating is tailored by varying any one or moreoperating parameter selected from the group consisting of laser pulselength, laser pulse energy, laser intensity, and laser spot size. 18.The system of claim 17 wherein: the laser pulse length is from about 5femtoseconds to about 100 microseconds; the laser pulse energy is fromabout 0.001 mJ to about 10 J; the laser intensity is from about 10⁴W/cm² to about 10¹⁵ W/cm²; and the laser spot size is from about 1micrometer to about 5 millimeters.
 19. The system of claim 18 whereinthe thermal barrier coating comprises a thickness of from about 50microns to about 750 microns.
 20. A system for applying a thermalbarrier coating to a superalloy substrate comprising: two targets forsupplying a material for making the thermal barrier coating, a firsttarget comprising zirconium oxide and a second target comprising yttriumoxide; two Nd:YAG lasers, one laser operably directed toward each of thetargets for liberating atomic particles from the targets; and a plasmatorch for generating a plasma for accelerating and depositing the atomicparticles onto the superalloy substrate as the thermal barrier coatingcomprising about 92% by weight zirconium oxide and about 8% by weightyttrium oxide.